into the Thick coal. So far, however, from there being a thousand feet of Coal-measures between the bottom of the Permian and the Thick coal, there are not more than 520 feet at the Lewisham pit, 350 feet at the Lyng colliery, 330 feet at Messrs. Davis's pits at Spon-lane, and only 30 feet or 40 feet at the Heath pits of Lord Dartmouth. We have in these facts a clear case of decided unconformability between the Permian beds and the Coal-measures. We see that after the Coal-measures had been deposited they had suffered largely and very irregularly from denudation, several hundred feet of strata having been removed at one place which were left untouched at another, before the Permian beds were begun to be deposited on them. The belief of this denudation having taken place is confirmed by the appearance of angular and rounded fragments of Coal-measure rocks and pebbles of coal being found in the bottom beds of the Permian rocks at Quarry Hill near Halesowen, and at the Heath pits, West Bromwich (see Vertical Sections. Sheet 17, No. 17). We can hardly suppose this denudation to have taken place without a previous elevation and disturbance of the beds, although, as in the other case of the Silurian rocks, this elevation may have been so steady and equable that it did not cause the Coal-measures very sensibly to incline from a horizontal position.[1]
It is perhaps rash to generalise from the very scanty data we possess as to the precise relations between the Permian and Coal measures. On so important a point, however, it is. I believe, a duty to state every opinion that may be fairly arrived at. I will therefore state, as my belief, that not only near West Bromwich, but generally in South Staffordshire and the adjoining counties, the Coal-measures suffered very greatly from denudation before the deposition of the Permian, and that the red sandstones of that formation were largely deposited in hollows and excavations worn in the Coal-measures by this denudation; and, moreover, that this excavation and denudation had in places proceeded to the length of being continued right through the Coal-measures down to the rocks below.
It may be useful, in order to arrive at a right understanding of this subject, if we discuss in detail the operations that were carried on at the celebrated Heath pits of Lord Dartmouth at West Bromwich. For this purpose we have the data given in Sir R. Murchison's Silurian System, and others partly collected by myself, but principally received from Mr. H. Johnson, Mining Surveyor, of Dudley. In the section published as No. 17, Sheet 17, of the Vertical sections, the actual shaft is drawn to scale, with the measures passed through, as given in the Silurian System, p. 476. On the left or west side of the shaft the section is copied from one lent by Mr. Johnson, which he compiled from the accounts of the men engaged in the sinking of the shaft, and corrected from his own measurements; and on the east side of the
- ↑ A dip of even 3° is often hardly perceptible either to the eye or to the clinometer, although it produces very large results if continued over a wide space. A bed dipping at 3° for the space of 3 miles will be 839 feet lower on the "deep" than it is on the "rise" side.
